1. Field of the Invention
The present invention relates to an air bag door structure in an instrument panel of a car and particularly relates to an air bag door structure integrally backed with a door reinforcement member in the rear side of an air bag door opening portion of an instrument panel.
2. Description of the Related Art
As shown in FIGS. 17 and 18, an air bag device provided in the front passenger side of a car is designed so that a folded air bag A contained together with an air bag actuating member (inflator) I in an air bag container C is stored in the inside of an instrument panel 150 in front of the front passenger's seat. The upper portion of the air bag container C is formed as an opening portion O for expanding the air bag A into the car room. A mount portion 154 to the instrument panel 150 is provided in the outer circumference of the opening portion O.
The air bag container C is fixed to the rear surface of the instrument panel 150 through the mount portion 154. The opening portion O is covered by an air bag door portion D formed integrally with the instrument panel 150.
A break portion 151 made from fragile portions such as V-grooves, slits, or the like, is formed in the instrument panel 150 so as to be substantially U-shaped or square-shaped so that the air bag door portion D of the instrument panel 150 is defined by this break portion. The air bag door portion D is integrally backed with a door reinforcement member 153 such as an aluminum plate, an iron plate, or the like, having a hinge portion 152 in the rear side of the air bag door portion D partitioned by the break portion 151.
In the air bag device configured as described above, the inflator I is operated so that the air bag A expands instantaneously when the car is subjected to large impact. As a result, the air bag door portion D is forced open from the inside, so that the break portion 151 is cleaved. As a result, the air bag door portion D is opened through the hinge portion 152. The air bag A is expanded into the car room through the opening portion O.
In this structure, the air bag door portion D is formed integrally with the instrument panel 150. Accordingly, there arises an advantage in that the external appearance is cleaner compared with an air bag door portion molded and mounted separately.
However, when, for example, the break portion 151 is substantially U-shaped as shown in FIGS. 19 and 20, transmission between traverse (left and right) cleavage 151a and longitudinal (front and rear) cleavage 151b is not smooth because of corner portions 155, or the like, of the break portion 151 at the time of cleavage. As a result, the cleavage gnaws into the instrument panel in the directions E1 and E2 so that the expansion of the air bag door portion D is resisted by the gnawed portions F1 and F2.
Particularly, since the area around the hinge portion side of the air bag door portion D is reinforced by the door reinforcement member 153 and the instrument panel in the outer circumference of the break portion 151 in the door opening portion side is not reinforced, the cleavage occurs more easily in portions other than the break portion 151.
Furthermore, as shown in FIG. 21, the air bag door portion D is backed with the door reinforcement member 153, but it is generally the case that the reinforcement member 153 is integrally fixed to the rear of the instrument panel 150 by providing bosses 156 in the rear of the air bag door portion D of the instrument panel 150 and by thermally caulking the bosses 156 through the reinforcement member 153. Therefore, it is preferable that the bosses 156 and the break portion 151 are provided so as to be as far from each other as possible to prevent the fragile break portion 151 from being affected by heat. As a result, however, the break portion 151 is pulled by the bosses 156 when the air bag door portion D is opened. Thus, there is a risk that bending G as shown in FIG. 22 may occur in the air bag door portion and that the air bag door portion may be cleaved in portions other than the break portion 151 as represented by the reference character H in FIG. 23.